T973: add build script for node_exporter package

[rebortg]

Change Summary

Add build script for latest node_exporter version.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes)
• [ ] Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• [ ] Other (please describe):

Related Task(s)

https://vyos.dev/T973

Component(s) name

service monitoring node-exporter

Proposed changes

How to test

after install the binary is in /usr/sbin/node_exporter

Checklist:

• [x] I have read the CONTRIBUTING document
• [x] I have linked this PR to one or more Phabricator Task(s)
• [x] My commit headlines contain a valid Task id
• [ ] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly